Control system



H. D. JAMES;

CONTROL SYSTEM.

APPLICATION FILED MAYZ7,1918- Patented Sept; 27,1921.

2 SHEETS-SHEET L an M 62 WITNESSES:

X7 Mz lNVEN TOR fienryOJzmes.

ATTORNEY 2 SHEETS-SHEET 2.

4 Fig-5- A Q m n H. D. JAMES.

CONTROL SYSTEM..

APPLICATION FILED MAY 27. 1918. 1,392,056, PatentedSept. 27, 1921.

1 INVENTOR Hemyfldk mm ATT( )RNEY jvlfNEssEs I HENRY D. JAMES, 013EDGEWOOD PARK,

HOUSE ELECTRIC & MANUFACTURING COMPANY, A CORPORATION VANIA.

PENNSYLVANIA, ASSIGN OR TO WESTING- F PEN N SYL- CONTROL SYSTEM.

Application filed May 27,

To all whom it may concern Be it known that I, HENRY D. JAMEs, a citizenof the United States, and a resident of Edgewood Park, in the county ofAllegheny and State of Pennsylvania, have invented a new and usefulImprovement in Control Systems, of which the following is aspecification.

My invention relates to systems of control of general application, butmore particularly to systems of control for electric motors, such, forexample, as motor-accelerating systems involving main switches orcontactors designed to close in succession to shunt a resistor. Insystems of the character above designated. each contactor is customarilyprovided with an auxiliary switch or a relay for governing the closingof the contactor, and, in order to avoid injuring the motor by excessivecurrent, each contactor is adapted to close before the relay forcontrolling the next succeeding contactor can operate.

()ne object of my invention is to provide an improved motor-acceleratingsystem of the type indicated.

Another object of my invention is to pr ovide a system, the parts ofwhich may be standardized, thus effecting a saving in manufacture andmaintenance.

A further object of my invention is to provide a novel acceleratingsystem in which the motor may be disconnected from the line, and thenreconnected, at reduced speed, without fear that the motor will beconnected directly across the line with all starting resistance out ofcircuit, and the motor windings thereby injured.

According to my system, I arrange a relay or a plurality of relays inparallel circuit with the accelerating resistor of an electric motor,these relays being adapted to be successively actuated, due to adecreasing magnetism caused by the acceleration of the motor and theshort-circuiting of portions of the resistor, to closed position tocause the closing of contactors which control the short-circuiting ofthe resistor. The relays and contactors are interlocked mechanically orelectrically for a purpose to be described below.

Other objects of my invention will be apparent from the followingdescription, when taken in connection with the accompanying drawings, inwhich Figure 1 is a diagrammatic View of a system, arranged accordingSpecification of Letters Patent.

Patented Sept. 27, 1921.

1918. Serial No. 236,937.

to my invention, for accelerating a motor; g. 2 1s a similar View of amodification; Figs. 3, 4 and 5 are, respectively, a side and an endelevation and a plan view of a preferred switch employed in connectionwith the systems of Figs. 1 and 2; Fig. 6 is a diagrammatic view ofstill another modification; and Fig. 7 is a diagrammatic viewillustrating my invention as applied to an alternating-current system.

Referring to Fig. 1, a motor, the armature of which is shown at 1 andthe shunt field-magnet winding at 2, is connected be tween lineconductors 3 and 4, separated by a line contactor 5, with a regulatingresistor 6 normally in series with the armature 1. A master controller 7controls the closing of the switch 5, through an energizing coil 8, byclosing the contact 9. One or more contactors 10, 11 and 12 (three areillustrated), control the shunting of successive portions 13, 1-1 and'15 of. the regulating resistor 6, through the medium of energizingcoils 19, 20 and 21, which energization is effected by the mastercontroller 7 closing the contact members 16, 17 and 18. A coil 22 isconnected in parallel circuit With the resistor 6. and a second coil 23is connected across the terminals of the armature 1, the coil 23 beingin circuit with a high external resistance 24. which may be embodied inthe coil itself if desired. The energizing of the coil 22, as explainedbelow, causes the successive closing of relays 25, 26 and 27 inaccordance with the strength of the current passing through the coil 22.The coil 19 and the relay 25 are series connected in a circuit extendingfrom the line conductor 3, through the contactor 5, the conductor 28 andthe contact member 16, to the line conductor 4. The coil 20 and therelay 26. as well as the coil 21 and the relay 27, are in parallelrelation with the coil 19 and the relay 25.

A preferred form of device for use in the system of Fig. 1, illustratedin Figs. 3, 1 and 5, forms the subject matter of a copendingapplication, Serial No. 241,259, filed June 31, 1918. De Camp, relay,and assigned to the Vestinghouse Electric a. Manufacturing Company.Briefly. it comprises a coil, the current flowing through which createsa magnetic field which causes an armature to close. thereby releasing a.plurality of armatures. each bearing a relay contact member. Theselatter armatures tions, but, owing to the magnetic field abovementioned, the power of the springs is ternporarily overcome until themagnetic flux,

produced by the electric current, sinks to predetermined values. Thearmatures are thus operated in'succession, depending for their operationon the period of acceleration of the motor.

An insulating panel 29 carries two brackets 30 and 31 supporting thecoils 22 and 23 which, when energized by current flowing through them,create magnetic fields for attracting an armature 32 and any desirednumber of additional armatures 33, 34 and 35. A compression spring 36 isadjustably mounted upon a non-magnetizable rod 37 slidably mounted inprojections 38 and 39 which are rigidly connected to or are integralparts of the bracket 31. The

projections 38 and 39 serve also as pole pieces for the armatures 32 and33, 34 and 35,

respectively. A bar 40 is rigidly connected to the rod 37, and normallyengages the armatures 33, 34 and 35. The spring 36 thus normallymaintains the armatures 33, 34 and in open position, with the members41, which are carried by these armatures, in contact with the pole piece39. The members 41 are preferably of non-magnetizable material toprevent freezing.

The armature 32 is provided with brackets 42, which are pivotallymounted upon the bracket 30, and is normally retained in the broken-lineposition, (Fig. 3), by a weak spring 43. The bracket 30 supports anon-magnetizable, U-shaped member 44, between the arms of which arepivotally mounted the armatures 33, 34 and 35, which carry,respectively, the movable contact members 45, 46 and 47 of the relays25, 26 and 27, shown in Figs. 3, 4 and 5 as closed.

The stationary contact members 48, 49 and 50 of the relays 25, 26 and 27are mounted upon the insulating ,panel 29. Springs 51 are attached tolongitudinally adjustable members 52 and to the other ends of themembers 41. The pole piece 39 is provided with longitudinally adjustablemembers 53 to regulate air gaps 54 between these members and thecorresponding armatures. By means of this adjustment, or by means of themembers 52, the action of the magnetic flux produced by the coils 22 and23 maybe so regulated that the armatures 33, 34 and 35 will be operatedin proper sequence.

The operation is as follows: Upon the actuation of the master controller7 to. the position a, the coil 8 is energized to close the linecontactor 5, which. completes the 22 creates a magnetic field whichattracts the armature 32 to the pole piece 38. The rod '37 is thereuponpressed inwardly, in opposition to the force of the spring 36, forcingthebar 40 away from the armatures 33, 34 and 35. The motion of thearmature 32 is from the broken-line to the full line position of Fig. 3.If the current is above a previously selected safe value, the flux ofthe magnetic field will overcome the forces of the springs 51 and thearmatures will remain with the stops 41 in engagement with the polepiece 39. As the motor accelerates and the current begins to die down,the magnetic flux set up by the coil 22 becomes weakened. After a time,when the flux has decreased to a predetermined value, the spring 51attached to one of the armatures, say the armature 33, will overcome theflux of this field, so that the relay 25 will be closed. The time whenthis operation occurs depends upon the air gap 54 and the tension of thespring 51. The relays 26 and 27 however, remain open.

If the master controller 7 has been actuated to the position b, acircuitmaybetraced from the line conductor 3 through the contactor 5, theconductor 28, the relay 25, the coil 19 and the contact 16, to the lineconductor 4. The closing of this circuit ener- "gi z'es the coil 19,which causes the closing on the contactor 10, and this, in turn, createsa shunt circuit for the portion 13 of the resistor 6. The motor thenfurther accelerates to decrease the-voltage across the terminals of thecoil 22 and thus weaken the magnetic field in the neighborhood of thiscoil, which permits the closing of the relay 26. A circuit is then made,assuming that the master controller occupies the position 0, from theline conductor 3, through the contactor 5, the conductor 28, the relay26, the coil 20 and the contact 17 to the line conductor 4. The coil 20,thus becoming energized, causes the closing. of the contactor 11, andthe consequent shunting of the resistor 14. After the motor has furtheraccelerated, the magnetic field surrounding the coil 22 is againweakened and the relay 27 is closed, creating a circuit, if the mastercontroller occupies the position (2, from the line conductor 3, throughthe conductor 28, the relay 27 the coil 21 and the contact 18 to theline conductor 4, thereby causing the energization 'of the coil 21 andthe closing of the contactor 12. The resistor 6 is then entirely shuntedfrom the armature circuit and the armature 1 .is connected directlyacross the line. i i

The shunting of the entire resistor- 6 deenergizesthe coil 22- and tendsto release the armature 32 and open the relays 25, 26 and 27. This isprevented by the coil 23, which is ener zed by the'counter-electromotive force o the armature 1.

The master controller 7 may obviously be actuated step-by-step or to theposition (I in a single step. In the latter event, the above-describedoperations will take place automatically and in sequence.

It, now, the motor remaining at high speed, the master controller 7 beactuated to the off position, as illustrated, denergizing the coils 8,19, 20 and 21, the con ta'ctors 5, 10, 11 and 12 open. On account of thecoi'inter-electromotive force in the coil 23, however, the relays 25, 26and 27 will remain closed for a limited time, whereby, upon againactuating the controller 7 during this time, the coils 8, 19, 20 and 21becoming reenergized, the contactor 5 will close to reestablish themotor circuit, and the contactors 10, 11 and 12 will immediately closeto again shunt the resistor 6. This tends to have the effect of suddenlythrowing the armature 1 into the line circuit without any resistance inseries with it. To prevent this happening, therefore, the contactor 10and the relay 26 should be mechanically interlocked, as at 55, in suchfashion that, when the contactor 10 is open, the relay 26 will also beopen, thereby keeping open the circuit of the coil 20 to preventtheclosing of the contactor 11. Similarly, the contactor 11 and the relay27 should be interlocked so that, when the contactor 11 is open, therelay 27 will be kept open. The contactors 10 and 11, however, are freeto close, leaving the relays 26 and 27 open.

Thus in the contingency referred to, upon the actuation of the mastercontroller 7 to the off position, although the relay 25 will remainclosed because of the counterelectromotive force in the coil 23, therelays 26 and 27 will be open because the contactors 10 and 11 are open.If the circuit be now reestablished by the closing of the master switch7, the relay 25 being closed, the coil 19 will be energized to cause theclosing of the contactor 10. Not until the contactor 10 closes, however,can the relay 26 close. The closing of the relay 26 will cause theclosing of the contactor 11 through the energization of the coil 20. Notuntil the contactor 11 closes can the relay 27 close to cause theclosing of the contactor 12. The closing of the contactors 11 and 12will de pend upon the speed of the motor, as previously described, forthe magnetic field created by current in the coil 23, thougn strongenough to maintain the relays 25. 26 and 27 in closed position, is notstrong enough to effect their closing in the first instance.

The interlock may be electrical instead of mechanical. In Fig. 2 I haveshown one arrangement for electrically controlling the operation of thecontactors 10 and 11 and the relays 26 and 27. The contacts 16, 17 and18 have been omitted from this drawing, but may be inserted in thesystemif desired.

The coil 19 is connected in circuit as before described. The circuit ofthe coil 20, however, is made from the line conductor 3. through theconductor 28 and the relay 2G to the'connecting point 57 of theresistors 13 and 14:. hen the resistor 13 is included in the circuit,the voltage is not sufficient to energize the coil 20, and the contactor11, therefore, remains open.- hen the contactor 10 is closed, thecircuit is completed to the line conductor 4 through this contactor, andthe coil 20 becomes sufficiently energized to close the contactor 11.Similarly, the coil 21 is connected, at 58, in a circuit which includesthe resistors 13 and 14, except when the contactor 11 is closed, therebydelaying the closing of the contactor 12 until the contactor 11 isclosed.

In other unit-switch systems now in use, no positive means is providedfor always operating the relays, and, therefore, the contactors, at justthe proper time. In'systems employing mechanically interlockedcontactors and relays, for example, the current does not always risewith sufiicient rapidity to hold the relays from closing, and there is,consequently, at such times, nothing to limit. the closing but theinherent time element of the relays themselves. Systems employing theordinary series-lockout switch ave proved unsatisfactory for the reasonthat such a switch operates between fixed current limits only, and thecurrent sometimes drops so rapidly through these limits that the switchhas not time to act, and, accordingly, fails to close. It will be seenthat, in my system, the value of the current determines the proper timeof closing. All that is necessary is that this time be previouslyselected by proper design. I

It is further to be noted that my system does not depend on theoperation of a current which is successively brought back to the samepeak and then allowed to fall. In the ordinary series relay, eachsuccessive peak is relied upon to build up the magnetism for actuatingthe next following relay. In my system, the magnetism is continuallyfalling according to a substantially straightline law. The closing ofsuccessive contactors causes no measurable rise in the magnetism. Theadvantage of a system which depends, for its operation, upon acontinually falling voltage is that. at no time during the operation, isit necessary to depend upon magnetism building up.

This advantage follows directly from connecting the coil-22 across theterminalsof the resistor 6. It is possible. of course, to employ asystem in which the coil 22 shall be connected in series with'theresistor. hether the arrangement be parallel or series, the motorciu'rent decreases from a high peak to a low peak every time that aportion of the resistor is shunted. If the coil 22 be connected inseries with the resistor, and the current peaks have the same value, therelays 25, 26 and 27 will close simultaneously. To avoid thissimultaneous closing, the current may be arranged to drop tosuccessively lower values, but, it is found that these values are sonearly alike that the relays 25, 26 and 27 must be set to operate atvalues so close to each other, that there is no danger of improperoperation. Otherdifi'iculties in practical operation also pertain to theseries arrangement. The arrangement of the shunt coil, as shown, permitswidely different values of magnetism corresponding to the same motorcurrent.

Another advantage of the shunt-coil arrangement is that, with shuntcoils, standardization is possible, for the same coil may be employedfor all applications and is independent of the size of the motor. If aseries coil be employed, different motors and applications require theuse of separately designed coils. 7

It should be emphasized that the operation of my system is, in no way,dependent upon the particular switch illustrated in Figs. 3, 4c and 5.Separate relays, like those illus trated in Fig. 1 of the De Campapplication for relay, above referred to, may, of course, be employed;but it is possible to so design my system as to make it operative withany relay. ll have illustrated such a system in Fig. 6.

In this system, the individual relays 25, 26 and 27, of any ordinarytype, are normally closed instead of, as in the De Camp relay, normallyopen. If desired, a single relay having three armatures may be-used. Thecoils 22, 22 and 22 for controlling the operation of these relays areconnected in series (as shown) orparallel, in series with a resistor 59(which may be omitted), across the terminals of the resistor 6. If asingle relay having three armatures is used, the three coils 22*, 22 and22 will be replaced by a single coil, as in Figs. 1 and 2. The relay 25is provided with an additional pair of stationary contacts 60, adaptedto be bridged in the upper position of the relay to close a circuit forthe coil 8 across the line conductors 3 and 4. A switch 61 ismechanically interlocked with the line contactor 5 to short-circuit thecontacts 60. The master controller 7 may correspond to either of thetypes illustrated in Figs. 1 and 2.

The closing of the controller 7 creates a circuit for the coils 22, 22and 22 which extends from the line conductor 3, through the armature 1,the resistor 59 and the controller 7, to the line conductor 4. Therelays 25, 26 and 27 are immediately opened. The opening of the relay 25causes the closing of 65 a circuit which extends from the lineconaaeacae ductor 3, through the coil 8, the contacts 60 and thecontroller 7, to the line conductor The consequent energization of thecoil 8 causes the closing of the line contactor 5 and the switch 61. Theformer establishes the motor circuit, and the latter short-circuits thecontacts 60 as follows: from the line conductor 3, through the coil 8,the switch 61 and the controller 7, to the line conductor 4. The coil 8will thus remain energized to maintain the contactor 5 and. the switch61 closed, even though contact be broken at 60.

The coils 22, 22 and 22 of the relays 25,26 and 27 are, as before, sodesigned as to cause the relays to close successively, according to adecreasing magnetism; or, if a smgle coil is employed, the relays may beof different weights, or may be actuated by springs of differentstrength. The relay 25 closlng first, a circuit is established from theline conductor 3, through the coil 19, the relay 25, and the contactor5, to the line conductor a. The consequent energization of the coil 19causes the contactor 10 to close and the resistor 13 to be shunted fromthe armature circuit. In similar fashion, when relays 26 and 27 closelater, as previously described in connection with Figs. 1 and 2, theremaining portions of the resistor 6 will be short-circuited and thearmature will be connected directly across the line. The necessity for aholding coil 23 is thus obviated.

It should be noted that the system of Fig. 6, like the systems of Figs.1 and 2, insures that the motor shall not be connected across the linewithout starting resistance. The line contactor 5 cannot be closed untilafter the relay 25 has been raised to break the circuit of the coil 19;and the circuit of the coil 19 cannot be made, even though the relay 25is in its lower position, until after the line contactor 5 has beenclosed.

' A study of the system of Fig. 6 will make evident another advantageof: the shunt-coil arrangement. For successful operation, it isnecessary that the relays 25, 26 and 27 be open before the motorcommences accelerating. This may be effected mechanically, as by thespring 36, or'(assum1ng that the coils 22", 22? and 22 of Fig. 6 are relaced by a single coil) electrically by line vo tage. If the coil werearranged in series with the resistor, itl would not be possible to openthe relays by line voltage without,

at the same time, starting the motor.

My invention is by no means limited to direct current, as will be madeevident by reference to Fig. 7, showing an accelerating system for awound induction motor, the primary windings, connected in circuit withthe line conductors 3 3 and 3 of a threephase transmission line, beingillustrated at 62, and the secondary winding at 63. The.

. ed in the circuit of one of the secondary leads 4*, this switch 64being adapted to close a circuit between two of the primary leads 3 and3", which includes, in parallel relation, the relays 25, 26 and 27 andthe corresponding actuating coils 19, 20 and 21 of the contactors 10, 11and 12. The line contactor 5 may be closed in any desired way, as bymeans of the master controller 7 closing a circuit for the coil 8between two primary leads 3 and 3".

Upon the actuation of the controller 7 to energize the coil 8, the linecontactor 5 is closed to connect the primary windings 62 in circuit withthe three-phase transmission line. Current then flows between the leads4*, 4 and 4 of the secondary winding 63, through the resistor 6. Currentflows also through the coils 64 and 22, which are connected in thecircuit extending from one terminal of the lead 4', through the coil 64,and the coil 22, to the other terminal. The switch 65 therefore closes.With the fall of current in the resistor 6, and, therefore, also in thecoil 22, the relay 25 first closes, establishing a circuit from the lineconductor 3 through the switch 65, the coil 19 and the relay 25 to theline conductor 3*. The coil 19 is therefore energized to close thecontactor 10 and short-circuit the portion 13 of the resistor 6.Similarly, the relays 26 and 27 are later .closed to energize the coils20 and 21 to cause the short-circuiting of the remainder of theresistor. The closing of the relay 27 establishes also a circuit for theholding coil 23 extending from the line conductor 3 and, through thecoil 23 and the relay 27, to the line conductor 3*.

Although I have illustrated my invention as applied to amotor-accelerating system, it will be understood that it may be equallywell applied to other systems including resistors. In some systems,such, for example, as those for heating With eIectric furnaces, theresistor forms substantially the whole circuit, in which case theenergization of the coil depends upon the drop in voltage of the wholecircuit.

'VVhile the motor has been illustrated as arranged for operation in onedirection only, it will be understood that my invention is equallyapplicable to systems in which reversing mechanism is employed for thepurpose of operating the motor in opposite directions, and to othersystems, such assys;

tems that involve dynamic-braking, field control, etc.

It will be understood that I do not limit my system to the specificforms shown, or to the specific switch devices illustrated in thefigures,-but that any equivalent system and any equivalent switchdevices maybe employed without departing from the spirit of my inventionas claimed.

I claim as my invention:

1. In a control system, the combination with a resistor, and means forsuccessively shunting a plurality of portions of said resistor, of meanscomprising a single coil dependent upon the voltage across said resistorfor controlling said shunting means.

2. In a control system, the combination with a resistor, and means forsuccessively shunting portions of said resistor, of means comprising asingle coil dependent upon the voltage across said resistor and switchmembers controlled thereby for controlling said shunting means.

3. In a control system, the combination with an electric circuitincluding an electric motor, a resistor, and a plurality of switches forsuccessively shunting portions of said resistor, of means comprising asingle coil dependent upon the electrical conditions of said resistorfor controlling the closing of said switches during the operation of themotor.

4. In a control system, the combination with an electric circuitincluding a resistor, and a plurality of electromagnetic switches forshunting portions of said resistor, of means dependent upon the portionof said resistor remaining in said circuit for successively effectingthe operation of said switches.

5. In a control system, the combination with an electric circuitincluding a resistor, a switch for shunting a portion of said resistor,and means for closing said switch, of means dependent upon the voltageof said resistor for temporarily rendering said first means inoperative.

6. In a control system, the combination with an electric circuitincluding a resistor,

ing actuating coils, of means dependent.

upon the voltage across said resistor for delaying the closing of aswitch by preventing the energization of its actuating coil for aninterval of time after the previous switch has closed.

50 1 the coil is energized, means for rendering of said resistor, saidswitches havin 'actuating coils, and of means for contro ling theenergization of sald coils, said means comprlsinga coil energized inaccordance with the voltage across said resistor, and relay membersoperable at different degrees of energization of said coil forcontrolling the circuits of said actuating coils.

9. In a control system, the combination with anelectric circuit includina resistor, a plurality of switches for shunting portions of saidresistor, and controlling means having different power values foreffecting the closing of each of said switches, of means for temporarilyrendering said controlling means inoperative, and for renderin saidcontrolling, means successively operat1ve..

I 10. In a control system, the combination with an electric circuitincluding a resistor, a plurality of switches for shunting portions ofsaid resistor, and means for normally maintaining said switches in openposition, of means for successively closing said switches upon saidfirst means becoming successively weakened.

11. In a control system, the combination with an electric circuitincluding a resistor,

' and a plurality of electromagnetic switches for shunting saidresistor, of means comprising a single coil in parallel with saidresistor for creating a magnetic field,:a'nd means controlled by said.field and operable at difi'e'rent degrees of strength thereof foreflecting the operation of said switches.

12. In a' control system, the combination with an electric circuitincluding a resistor, and a plurality of switches for successivelyshunting portions of said resistor, of a coil in parallel circuit withsaid resistor, and means dependent upon the strength ofthe current insaid coil for effecting the successive operation of said switches.

13; In a control system, an electric circuit including a coil, alurality of switches, means for normally eeping said switches open,means for closing said switches, means rendering said,first meansinoperative when said second means inoperative when the co is energized,"and means for rendering said said switches w en'said coil is energizedbe- 14. In a control system, the combination .witha resistor, and aplurality .of'switches for successively shunting portions 'of saidresistor, of a coil connected across the ter I minals'of said resistor,and means dependent upon the strength of the current in said coil andoperable at progressively decreasing values thereof to control theoperation of said sively operating said relays when the said currentfalls progressively below predetermined values.

16. In a control system, the combination with a resistor, a plurality ofswitches for shunting portions of said resistor, and a series of relaysfor controlling the successive operation'of said switches, of a meanscomprising a single coil connected across the terminals of said resistorfor controlling the operation of said relays.

17. In a motor-control system, the combination with. a motor armature, aresistor in circuit therewith, and a pluralityof switches havingactuating coils for successively shunting portions of said resistor, ofa plurality, of relays adapted to be closed to energize said coils, 'andmeans for preventing suflicient energization of one of said coils toclose the corresponding switch when a prior switch is open.

18. The combination with a motor having a resistor, and a plurality ofswitches having actuatingcoils for short-circuiting portions of saidresistor, of a relay' for controlling one of said actuating. coils, saidrelay an said one coil being connected in a circuit including a portionof said resistor controlled by another of said switches, and means forshort-circuiting said portion of said resistor controlling theenergization of each of said coils, each of several of said relays andthe coil which it controls being connected in a circuit including ,a'portion of said resistor -when one of said switches'is open, saidcircuit including said switch and excluding said portion of saidresistor when said switch is closed,said circuits being arranged so asto prevent the closing of said swltches when said portions of saidresistorsare included in said relay circuits. j In a motor-controlsystem, the combination with a circuit including a resistor, and aplurality of switches for successively shunting portions of saidresistor, of means "dependent upon thevoltage across said resistor forkeeping said switches open, means for successively closing said switcheswhen ,the said voltage falls below predetermined values, and means forkeeping said switches v closed when said resistor has been completelyshunted; i

I has beenbro en.

21. In a control system, the combination with an armature, a resistor incircuit therewith, and a plurality of switches for successively shuntingportions of said resistor, of a coil in parallel with said resistor, asecond coil connected across the terminals of the armature, meansdependent upon the current in said first coil for successively closingsaid switches, and means dependent upon the current in said second coilfor retaining said switches in closed positions.

22. In a motor-control system, the combination with a motor armature anda resistor in circuit therewith, of: means for shunting said resistor,for maintaining said resistor shunted from said circuit, and forgradually reestablishin said shunt after said shunt 23. In amotor-control system, the combination with a inotor having an armatureand a resistor in circuit therewith, of means for shunting saidresistor; means controlled by the counter-electromotive force of saidarmature for keeping said-resistor shunted from said circuit, means forbreaking said shunt when said circuit is broken, and means for graduallyreestabhshing said shunt upon the closing of said circuit.

24. In a motor-control system, the combination with an electric circuitincluding a resistor, and a plurality of switches for successivelyshunting portions of said resistor, of a plurality of relays, meansdependent upon the speed of said motor for successively closing saidrelays to cause the closing of said switches, means dependent upon the seed of said motor for keeping said relays c osed, meansfor opening saidswitches when said motor circuit is opened, and means for thereuponopening some only of said relays, whereby, when the motor. circuit isagain established, the resistor can not be immedi-' ately entirelyshunted from the circuit.

25. In a motor-control system, the combination with a motor armature, aresistor in circuit therewith, and a plurality of switches forsuccessively shunt ng portlons' of said resistor, of a plurality ofrelays for closing said switches, means actuated by the counter;

electromotive force of said armature for keeping saidswitches and relaysclosed when.

said resistor is shunted, and an interlock between certain of saidswitches and the corresponding preceding relays for opening said lastnamed relays when said last named switches are open, whereby, when saidcircuit is broken and remade, the whole resistor will not be immediatelyreinserted into said circuit. v

26. In a motor-control system, the combination with a motor armature, aresistor in circuit therewith, and a plurality of switches forsuccessively shuntingportions of said resistor, of means in parallelcircuit with said resistor for controlling the closing of means fordisconnecting said armature from said source, and means for thereuponpreventing the operation of said second means until after the operationof said first means.

28. In a control system, the combination with an electric circuitincluding a resistor, and a switch for shunting said resistor, of meansin parallel circuit with said resistor for effecting the maintaining ofsaid switch in its open position during a predetermined period, andmeans for closing said switch at the end of such period.

29. In a control system, the combination with an electric circuitincluding a resistor, and a plurality of rela s for effecting theshunting of portions oi: said resistor, of a coilin parallel circuitwith said resistor, said coil when energized to a predetermined valueactuating said relaysto open position,

across said resistor and to the potential across the terminals of saidmachine for controlling the position of said switch.

31. The combination with a dynamo-electric machine, a resistor incircuit therewith,

and a plurality of switches for controlling said resistor, of meansresponsive to the drop in potential across said resistor and to thepotential across the terminals of said machine for controlling theposition of said switches.

32. The combination with a dynamo-electric machine and a resistor incircuit therewith, of means responsive to the drop in potential acrosssaid resistor and to the counter-electromotive force of said machine foreffecting the shunting of said resistor and for maintaining the shuntingof said resistor during normal operation of said machine.

33. The "combination with a dynamo-electric machine and a resistor incircuit therewith, of means responsive to the drop in potential acrosssaid resistor for effecting the shunting of said-resistor and responsivetothe counter-electromotive force of said motor for maintaining theshunting of said resistor. a r

In testimony whereof, I have hereunto subscribed my name this 29th dayof April,

HENRY D. JAMES.

